From yesterday’s post, Pemmican: The perfect primal stick-to-your-ribs survival food, Jimmy Cracked-Corn asks,
“I just don’t understand the science behind it staying fresh, as other articles say, “for decades”. It’s half fat. I’ve had rancid Crisco, rancid lard, even rancid vegetable oil. What makes pemmican store so well, long term?“
Answer: Jimmy, I believe the rendering process at low temps (240 and below) is the key to removing all the water out of the fat/tallow. Meanie bacteria can’t live without the water. The tallow, if rendered properly, actually acts as an anti-bacterial.
Here’s more info from PaleoHacks.com:
By rendering the fat, you remove all the water and protein. If you are rendering suet, you are left with a very high saturated fat tallow. Saturated fat is pretty stable stuff. If you protect rendered suet from light and water, it should stay edible for years.
Rancidity occurs three basic ways: via oxidation of unsaturated fatty acids (you avoid this by having a high saturated fat mix to start out with), via reactions with water, and via microbial digestion. Pemmican avoids all of those through rendering the fat, thoroughly dehydrating the meat and hopefully being stored in a waterproof container.
Related reading and research on pemmican: